Studies are under way in several lines: A) Relation of structure and function in human growth hormone: the action of specific enzymes on the structure and activity of human growth hormone, and on parts of he hormone set free by enzymatic action, are being studied in several in vivo and in vitro systems, with a view to establishing the minimum structural features required for activity. B) Highly purified monkey growth hormone is being prepared, in order to determine the amino acid composition and other characteristics of this primate hormone. C) Pituitaries from dogs are being fractionated by new procedures in order to prepare canine growth hormone, prolactin, and possibly other active principles.